The present invention relates to a splitter-type impeller, for example, provided for an inlet portion of a gas turbine to raise a pressure of a gas such as air, particularly, for guiding a gas sucked from a central side of the gas turbine by rotation of a turbine driving shaft to an outer peripheral side thereof and discharging it outward.
In a gas turbine, an air is compressed by a compressor coaxially disposed to a turbine driving shaft, and the compressed air is mixed with a fuel and burnt in a combustor to thereby obtain a gas of high temperature and high pressure. The obtained gas is then introduced into turbines and causes a driving force to rotate the turbines at a high speed. And the turbines are mounted to the turbine driving shaft (rotation shaft).
In general, for the impeller of this kind, it is required to ensure sufficiently large gas inlet area with the most effective number of blades in the whole impeller, not to cause a gas turbulent flow due to rapid change of the gas flow area and not to cause an efficiency loss due to rapid change of gas flow resistance.
FIG. 5 shows a general splitter-type impeller to be applied to a gas turbine, for example. Referring to FIG. 5, the impeller is provided with a rotary disc 2 having, at its central portion, a hub 1 for attaching the impeller to a rotation shaft, i.e turbine driving shaft, of a gas turbine. A plurality of full blades 3 and splitter blades 4 are disposed and fixed on one surface side portion of the rotary disc 2 alternately with predetermined spaces with each other along the rotating direction of the disc 2 in such a manner as that the full blades 3 and the splitter blades 4 provide curved shapes so that they are displaced more largely towards rotating direction at the outer peripheral side of the disc along its rotating direction.
As shown in FIG. 5 and FIG. 6, such full blades 3 and the splitter blades 4 have rear side edges 3b and 4b which are positioned to the outer peripheral edge sides 2a of the rotary disc 2. The full blades 3 have front side edges 3a positioned at portions near the outer peripheral surface of the hub 1 and the splitter blades 4 have front side edges 4a positioned slightly backward of the front side edges 3a of the full blades 3 in an axial direction.
The conventional splitter-type impeller of the structure described above and shown in FIG. 5 has an arrangement, as shown in FIG. 7, in which a gas inlet portion 5 is formed between the adjacent two full blades 3 with one splitter blade 4 interposed therebetween, so that sufficiently large inlet area is ensured. However, in such arrangement, an area of a gas flow passage 6, formed between the full blade 3 and the splitter blade 4, connected to the inlet portion 5 rapidly changes, likely causing a turbulent flow of the gas and causing gas flow loss due to a resistance of the passage, thus being inefficient.
FIGS. 8A, 8B and 9A, 9B represent modifications of such arrangement of the full blades 3 and the splitter blades 4. In the modification of FIGS. 8A and 8B, these blades are all formed as full blades 3 and the front side edge portions of such full blades 3 are cut off to provide cut-back portions 7 substantially in a triangular shape shown by dotted lines therein. In the modification of FIGS. 9A and 9B, the full blades 3 and the splitter blades 4 are alternately arranged along the disc rotating direction and only the full blades 3 are cut off to provide cut-back portions 7 substantially in a triangular shape shown by dotted lines.
According to the modification of FIGS. 8A, 8B the change of the flow area is made gentle to reduce the causing of the turbulent flow of the gas. However, in a case where the total number of the blades is made same as that shown in FIGS. 5 to 7, it is difficult to sufficiently ensure the area of the gas inlet portion 5 between the adjacent blades 3 in a view point of keeping operational efficiency of the whole impellers.
On the other hand, according to the modification of FIGS. 9A, 9B it is possible to ensure the sufficiently large area of the inlet portion 5. However, the area largely changes from the inlet portion 5 to the front end portion of the gas flow passage 6, resulting in the rapid change of the flow resistance, being inefficient.
As described above, for the impeller of this kind, it is generally required to ensure sufficiently large gas inlet area with the most effective number of blades in the whole impeller, not to cause a gas turbulent flow due to rapid change of the flow area and not to cause an efficiency loss due to rapid change of flow resistance. However, in the conventional impellers of the structures described above, there is provided no impeller sufficiently attaining all these functions, such as one function being attained, the other function being damaged.